1. Field of the Invention
This invention relates to expression vectors and, more particularly, this invention relates to the use of a viral genome as a vector for expression of foreign genes.
2. Brief Description of the Prior Art
Infection of susceptible cells with certain viruses, such as the Herpes Simplex virus (HSV), for example, typically results in shut-off of host protein synthesis. The shut-off occurs in two stages. The initial stage is very likely caused by a structural protein of the virus, and genetic studies indicate that this activity is not essential for virus growth. A second, irreversible inhibition occurs during the viral reproductive cycle as a consequence of expression of viral gene products. Available data based on chemical enucleation with actinomycin D or physical enucleation with the aid of cytocholasin B suggests that the inhibition is at least in part at the translational level.
Although Herpes Simplex virus, type 1 (HSV-1) was previously known to induce some host genes, and particularly foreign genes such as ovalbumin, for example, placed under control of viral regulatory regions and introduced into cells by transfection, their expression is selective and transient. It was previously believed that the inhibitory machinery of wild type virus would not permit sustained expression of a foreign gene introduced into the viral genome.